Abstract

Introduction: The objective of this project is to study the biological pathways activated in irradiated pancreatic cancer cells pre-treated with gold nanoparticles. Metallic nanoparticles emit Auger electrons and photoelectrons upon exposure to X-rays. When selectively delivered to tumors, these nanoparticles can locally enhance<?__anchored_object__ "ro_u170cins1e758"?><?__anchored_object__ "ro_u170cins1e759"?> the effects of radiation therapy. Previous in vitro work has primarily studied the effectiveness of nanoparticle-enhanced therapy, without elucidating the underlying biological mechanisms. Understanding the biological mechanisms (such as changes in gene expression) of how nanoparticles enhance radiation therapy can help in the further design of more effective nanoparticles.

Methods: Gold nanoparticle sensitization was tested using a human based pancreatic cancer cell line, Capan-1. Nanoparticle toxicity was tested using a combination of MTS and Alamar Blue assays after 24 hours of treatment. Gene expression was tested using immunofluorescence and western blot techniques. Cells were pretreated with 0.8 mg gold nanoparticles 24 hours prior to radiation. Cells were then harvested at various time points to determine how gene expression changes over time. Radiosensitization was carried out using a clonogic cell survival assay where cells were pretreated with 0.8 mg gold nanoparticles 24 hours prior to radiation and then re-plated at various densities 4 hours post radiation, and allowed to incubate for 14 days. Statistical differences were determined using ANOVA followed by student t-tests.

Results: The MTS and Alamar blue assays showed low gold nanoparticle toxicity towards cells up to a dose of 1mg for Capan-1 cells. Capan-1 cells pretreated with 0.8 mg gold nanoparticles for 24 hours prior to radiation showed lower cell survival than cells only treated with radiation. Western blots and immunofluorescence data showed that certain genes, such as γ-H2AX, were upregulated when pretreated with gold nanoparticles and irradiated compared to cells treated with radiation alone. It was also shown that γ-H2AX expression peaked around 30 minutes post radiation and then returned to basal levels after 24 hours.

Conclusions: Capan-1 cells experience more DNA damage when pretreated with gold nanoparticles than when only treated with radiation. γ-H2AX, which is a DNA damage-related protein, was upregulated in the combined dose showing that there was more DNA damage in the combined treatment. It was also shown that protein and gene expression analysis needs to be carried out at various time points post radiation to obtain a better understanding of the mechanisms involved in radiation induced damage to pancreatic cancer cells.